Looks like the commit 07173c3e(block: enable multipage bvecs) has uncovered iSER SQ sizing issue. Here is how I hit the issue: Created two luns under single target, then run the below script on each lun(parallelly). while [ 1 ] do iozone -i 0 -i 1 -I -+d -s 100000 -r 16384 -w done Then failures like below are logged in dmesg output, due to iw_cxgb4 SQ getting full at iSER target. "isert: isert_rdma_rw_ctx_post: Cmd: 00000000cb75342a failed to post RDMA res" This issue won't occur if luns are created on seperate targets. Also, the issue won't occur if I revert the multipage bvecs(07173c3e) changes at initator. Currently SQ is being sized this way: attr.cap.max_send_wr = ISERT_QP_MAX_REQ_DTOS:138 +1 + (ISCSI_DEF_XMIT_CMDS_MAX:128 * factor:3) = 523. I tried increaseing the SQ size and observed that the issue is not occuring when attr.cap.max_send_wr is 562. Looks like the avg length of RDMA READ/WRITE operations has increased after "multipage bvecs" changes. Queueing many large sized RDMA READ/WRITE WRs may cause backpressure and increases the chances of SQ getting full at provider driver. Notice the length(0x7f000 & 0x2000) of each RDMA READ operation below, for Before and After case. Before "multipage bvecs" RDMA READ: [ +0.001903] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x78] [ +0.000007] iser: iser_fast_reg_mr: lkey=0x8a41 rkey=0x8a41 addr=0x446166000 length=0x7f000 [ +0.000000] iser: iser_prepare_read_cmd: Cmd itt:120 READ tags RKEY:0X8A41 VA:0X446166000 [ +0.000007] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x6f] [ +0.000003] iser: iser_fast_reg_mr: lkey=0x13b51 rkey=0x13b51 addr=0x443b25000 length=0x7f000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:111 READ tags RKEY:0X13B51 VA:0X443B25000 [ +0.000022] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0xe] [ +0.000001] iser: iser_fast_reg_mr: lkey=0xa371 rkey=0xa371 addr=0x4461a4000 length=0x2000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:14 READ tags RKEY:0XA371 VA:0X4461A4000 [ +0.000004] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x79] [ +0.000003] iser: iser_fast_reg_mr: lkey=0x12f4f rkey=0x12f4f addr=0x4461a9000 length=0x7f000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:121 READ tags RKEY:0X12F4F VA:0X4461A9000 [ +0.000005] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x7d] [ +0.000003] iser: iser_fast_reg_mr: lkey=0xe040 rkey=0xe040 addr=0x447e67000 length=0x7f000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:125 READ tags RKEY:0XE040 VA:0X447E67000 [ +0.000021] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x7b] [ +0.000001] iser: iser_fast_reg_mr: lkey=0xb149 rkey=0xb149 addr=0x3d0366000 length=0x2000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:123 READ tags RKEY:0XB149 VA:0X3D0366000 [ +0.000004] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0xb] [ +0.000003] iser: iser_fast_reg_mr: lkey=0x1014c rkey=0x1014c addr=0x3d0368000 length=0x7f000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:11 READ tags RKEY:0X1014C VA:0X3D0368000 [ +0.000007] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x62] [ +0.000003] iser: iser_fast_reg_mr: lkey=0x7c3b rkey=0x7c3b addr=0x3d03e7000 length=0x7f000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:98 READ tags RKEY:0X7C3B VA:0X3D03E7000 [ +0.000021] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x11] [ +0.000001] iser: iser_fast_reg_mr: lkey=0x11752 rkey=0x11752 addr=0x3d6de6000 length=0x2000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:17 READ tags RKEY:0X11752 VA:0X3D6DE6000 [ +0.000004] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x77] After "multipage bvecs" RDMA READ: [ +0.002455] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x7d] [ +0.000006] iser: iser_fast_reg_mr: lkey=0x7991 rkey=0x7991 addr=0x3d2819000 length=0x7f000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:125 READ tags RKEY:0X7991 VA:0X3D2819000 [ +0.000005] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x7e] [ +0.000003] iser: iser_fast_reg_mr: lkey=0x8c9b rkey=0x8c9b addr=0x3d2898000 length=0x7f000 [ +0.000000] iser: iser_prepare_read_cmd: Cmd itt:126 READ tags RKEY:0X8C9B VA:0X3D2898000 [ +0.000003] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x7f] [ +0.000003] iser: iser_fast_reg_mr: lkey=0x856d rkey=0x856d addr=0x3d2917000 length=0x7f000 [ +0.000000] iser: iser_prepare_read_cmd: Cmd itt:127 READ tags RKEY:0X856D VA:0X3D2917000 [ +0.000004] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x1] [ +0.000002] iser: iser_fast_reg_mr: lkey=0x9b55 rkey=0x9b55 addr=0x3d2999000 length=0x7f000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:1 READ tags RKEY:0X9B55 VA:0X3D2999000 [ +0.000003] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x2] [ +0.000002] iser: iser_fast_reg_mr: lkey=0x86cf rkey=0x86cf addr=0x3d2018000 length=0x7f000 [ +0.000000] iser: iser_prepare_read_cmd: Cmd itt:2 READ tags RKEY:0X86CF VA:0X3D2018000 [ +0.000003] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x3] [ +0.000003] iser: iser_fast_reg_mr: lkey=0x8062 rkey=0x8062 addr=0x3d2097000 length=0x7f000 [ +0.000000] iser: iser_prepare_read_cmd: Cmd itt:3 READ tags RKEY:0X8062 VA:0X3D2097000 [ +0.000003] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x4] [ +0.000002] iser: iser_fast_reg_mr: lkey=0xc34b rkey=0xc34b addr=0x3d2116000 length=0x7f000 [ +0.000000] iser: iser_prepare_read_cmd: Cmd itt:4 READ tags RKEY:0XC34B VA:0X3D2116000 [ +0.000003] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x5] [ +0.000002] iser: iser_fast_reg_mr: lkey=0x8b6d rkey=0x8b6d addr=0x3d2195000 length=0x7f000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:5 READ tags RKEY:0X8B6D VA:0X3D2195000 [ +0.000003] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x6] [ +0.000002] iser: iser_fast_reg_mr: lkey=0xce56 rkey=0xce56 addr=0x3d0e14000 length=0x7f000 [ +0.000000] iser: iser_prepare_read_cmd: Cmd itt:6 READ tags RKEY:0XCE56 VA:0X3D0E14000 [ +0.000003] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x7] [ +0.000002] iser: iser_fast_reg_mr: lkey=0xba45 rkey=0xba45 addr=0x3d0e93000 length=0x7f000 [ +0.000001] iser: iser_prepare_read_cmd: Cmd itt:7 READ tags RKEY:0XBA45 VA:0X3D0E93000 [ +0.000002] iser: iscsi_iser_task_xmit: ctask xmit [cid 0 itt 0x8] Hence, I feel iSER target SQ is undersized and needs to be sized properly to hold max possible entries. I might be wrong. Please take a look. Thanks, Krishna.
